Delphi/Indy10 How to check an https URL is valid without downloading contents

Question

Previously the URL I needed to check was http and I used TidTCPClient to emulate the http protocol to determine the file at the web server existed. Now they have switched to https and I don't know how to do it.

Can I use TIdHTTP with the TIdSSLIOHandlerSocketOpenSSL hander, and then some Indy function to only determine the resource exists? I have OpenSSL installed.

Answer 1

Your existing TIdTCPClient code should continue to work if you simply assign a TIdSSLIOHandlerSocketOpenSSL to the client's IOHandler, change the client's Port to 443, and set the IOHandler's PassThrough to False. HTTPS is just HTTP over an SSL/TLS connection, it doesn't change HTTP itself.

But to answer your question, yes, you can switch to TIdHTTP if you want to. You can use the HTTP HEAD command (the TIdHTTP.Head() method) to check if a URL is valid without having to download a full resource.